The present invention relates to an exhaust gas purification control apparatus for an internal combustion engine.
According to a known exhaust gas purification control apparatus, air-fuel mixture control, exhaust gas recirculation control, and ignition timing control are separately and independently modified in response to electric output signals produced by a vehicle speed sensor and an engine speed sensor to provide optimum operation during low speed or light load and optimum operation during high speed or heavy load. According to another known exhaust gas purification control apparatus, air-fuel mixture control, exhaust gas recirculation control, and ignition timing control are separately and independently modified by pressure which varies with engine speed. These known apparatuses are designed to enhance fuel economy and endurability against heat.
However, with the known control apparatuses, since the air-fuel mixture control, exhaust gas recirculation control, and ignition timing control are separately and independently modified, there occurs a knocking due to an excessive increase in combustion speed, for example, when the air-fuel mixture is enriched and exhaust gas recirculation is decreased under the condition that the ignition timing is still advanced, thus deteriorating fuel economy and driveability.
Additionally, although the control apparatuses use an intake passage vacuum in the vicinity of the throttle valve, this intake passage vacuum no longer represents engine load under high engine load since it is greatly affected by manifold vacuum prevailing downstream of the throttle valve as the throttle valve opens.